Power from the Sun:
Solar, Hydro and Wind
Dennis Silverman
U. C. Irvine
Physics and Astronomy
Solar Power
Most of all energy we use comes or has
come from the sun.
Fossil fuels arise from fossil plants and
animals converted to carbon (coal), or
hydrocarbons (methane and petroleum).
We are 1/3 to 1/2 through the process of
burning hundreds of millions of years of
fossil fuel accumulations in two centuries.
Free Solar
The sun would heat the planet to 0° Fahrenheit without
the atmosphere.
The sun runs the greenhouse that keeps the earth
warmed up to an average of 58° F with the greenhouse
gas atmosphere.
It evaporates the oceans to provide the rain and fresh
water for crops and drinking water and hydropower.
It powers the weather to provide winds.
It grows our crops and forests through photosynthesis
Solar energy provides our daylight and moonlight.
It heats our buildings in the daytime, and the sea and
land hold heat for the night.
Pharoah Akhenaten and Queen Nefertiti
Monotheism of Aten, the Sun, 1353-1336 BC
Possible father of Tutankhamen (King Tut)
Solar Manipulation
The next best way to use solar is to modify
its effects.
– Reflective roofs to keep buildings cool
– Reflective windows to keep out direct sunlight
during the summer, and keep heat in during
the winter
– Windows and skylights for indoor daytime
lighting
Paint Your House White? Santorini
Direct Solar Energy
Mediterranean climates now using rooftop
or nearby solar water heating – Greece,
Israel, Japan. It is 80% efficient.
Solar clothes drying
Solar Photovoltaic Electricity
Silicon wafers doped to form photovoltaic cells
– Power is free, but
– Large wafers still thick and crystal grown as chips, so still
expensive
– Cost still 3 to 10 times as expensive as fossil fuel power
– Efficiency only 10 to 15%, so large areas needed
– Daily and yearly average only 1/5 of maximum power capacity
installed
– Don’t need storage if send excess power back over the grid
– Storage could be in charging car batteries or in hydrogen fuel, or
– Concentrate on using more energy during the daytime
– Silicon valley investigating thin film disk technology to make
cheaper
Unelectrified Areas
Two billion people do not have electricity
To save on kerosene lanterns, solar cells
with batteries and lcd lights have been
developed for nighttime lighting
Also used to charge freeway phones
California’s Million Solar Roofs
California SB1 (Senate Bill 1) to provide rebates to equip solar
power installations
Goal is 3 gigawatts solar by 2017
This could be 3 kw/household, at $9/watt is $27,000/household
Companies rebated per kwh generated
New homes must offer solar option by 2011
500,000 more homes can be added to generating electricity into the
power network
$2.8 billion CA cost, 30% Federal rebate, up to $18 billion total cost,
but for less average electricity than a nuclear plant at $2-3 billion.
Could only nearly pay if it brings down costs through economies of
scale,
or if it leads to technological breakthrough through research and
competition
Only $100 million for solar water heating
U. S. Solar Resources
U. S. Tracking Mirror Solar
Solar Trough Mirrors
Suitable For Large
Systems
Grid-connected
Power
30-200 MW size
Heats mineral oil to
hundreds of degrees
Then vaporizes a fluid
to drive a turbine
Dish with Sterling Engine
Modular
Remote Applications
Demonstration
Installations
High Efficiency
Conventional
Construction
Heat expands gas
and drives piston
Solar Tea? Tibet, Dreprung Monastery
Solar Tower
Suitable For Large
Systems
Grid-connected
Power
30-200 MW size
Potentially Lower
Cost
Potentially Efficient
Thermal Storage
Molten Salt heated,
averages out solar
Cost Of Energy*
(Max Lechtman)
Trough
2000
2010
2020
2030
Dish/Engine
11.8
7.6
7.2
6.8
*Cents/kWh in 1997 $
17.9
6.1
5.5
5.2
Tower
13.6
5.2
4.2
4.2
Hydropower
 Of the renewable energy sources that
generate electricity, hydropower is the most
often used. It accounted for 7 percent of
total U.S. electricity generation and 75
percent of generation from renewables in
2004
 Over one-half of the total U.S. hydroelectric
capacity for electricity generation is
concentrated in three States (Washington,
California and Oregon) with approximately
27 percent in Washington, the location of the
How Hydropower Works
World-wide, about 20% of all electricity is
generated by hydropower.
Glen Canyon Dam and Power Station
Aswan Dam on the Nile River
Wind Power - Mykonos
Clipper Ship
World Wind Capacity. Total now 74 Gigawatts
worldwide, with 65% in Europe. Market growing
at 32% a year. 3.3% of European electricity now
from wind. 1% of U.S. electricity.
Wind Generation Physics
 Power proportional to the cube of the wind velocity.
 (v² from Bernoulli pressure for force on wingshaped
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propeller, times a distance per second of rotating
propeller, which is proportional to v.)
Most of energy from small bursts.
½ of energy comes in 15% of the time.
Average capacity factor is 35% of the maximum.
Wind turbines best spaced 3-5 times the rotor diameter
perpendicular to the wind, and 5-10 times the diameter
parallel to the wind.
Virginia’s “Switzerland” Wind Power
Proposal
 39 towers of 400 feet height
 $2 million per tower at 1 megawatt

So about a 40 megawatt peak project
 Enough power for 15,000 homes x
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12,000 kwh/yr / 9,000 hours/year =
20 million watts average
Implies a 50% duty cycle
 To compare to a 1 gigawatt nuclear plant, would
require 50 such projects, or about 2,000 wind
towers and $2 billion.
England, Germany, Netherlands:
10 Gigawatt Foundation Project
 Proposal for 2,000 wind turbines of 5
megawatts each to make 10 gigawatts
 Could power more than 8 million homes
 Would cover 3,000 square kilometers
 In the southern North Sea
“Here Comes The Sun” (by George
Harrison) Conclusions
 “All renewable energy is local” Adapt to locally available
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sources of renewable energy
Energy conservation is still the cheapest form of making
energy available
In California, solar water heating is the next cheapest
source of energy
Hydro should be maintained
Solar arrays are efficient and should be supported
Wind power is about the cost of nuclear. Have to find the
right location. Siting a problem with views, noise, birds.
Nuclear power is omitted from renewable, but should be
included as it also is non-polluting for greenhouse gases.
Solar photovoltaic needs more research and
improvement, and is currently a wasteful investment.